The present invention relates to an endodontic instrument for preparing the root canal, provided both with a coupling for mounting on an endodontic contra-angle and with a conventional handle for manual use.
The morphological aims of a good preparation of the root canal can be summarized in the following items.
1. The canal must have a truncated-cone shape with a coronal larger planar face and an apical smaller planar face.
2. During preparation it is necessary to respect the original configuration of the canal.
3. A corollary of the preceding item is that the apical foramen must maintain the same spatial relationship with respect to both the root itself and to the paradental bone.
4. The apical foramen must be kept as small as possible.
One of the instruments used to prepare the canal is the so-called "reamer", a broaching instrument which is normally constituted by a bar which has a twisted triangular cross-section whose diameter increases constantly in the apical-coronal direction of the canal.
It is evident that the achievement of these aims with conventional instruments requires the operator to provide not only considerable manual precision and skill but also a great expenditure of time, with consequent costs for the patient.
The direct consequence of all this is that many operators prefer canal preparation methods which are simpler and more rapid, even if they are burdened by a higher percentage of failures; furthermore, rational and correct endodontics cannot be part of the practice of a dentist who performs so-called "social" dentistry, regardless of the good will and skill of the operator.
In order to provide the patients with a high-level endodontic service without however increasing the costs of these therapies, it would be necessary to use instruments mounted on the contra-angle, in order to save on canal preparation times.
However, it is known that with the currently available instruments it is not possible to achieve the above aims except to a minimal extent.
For example, one of the most severe problems of instruments mounted on a contra-angle is that in curved canals they cause the apical foramen to shift and become elliptical, and that they furthermore deform the apical portion of the canal, generating a truncated-cone shape with an apical larger planar face. The truncated-cone shape of the canal prevents the optimum condensation of the gutta-percha in that point, and a correct apical seal is consequently not ensured.